The 406 is an FE. Has the 428's bore and the 390 stroke. Don't know it's the 390 block or not. Always heard the I know the 352 and 390 are the same, and I believe the 410. but I had always heard the 428's were different. Don't know where the 406 fit's in all of this.
I thought the only diff. was the stroke between the 390 and the 428.The FE exchange rebuilding book says that they are all very similar,Different strokes,heads and manifolds.you can interchange alot . Dan
A 406 block externally looks a lot like a 390 block, however the cylinder walls are much thicker to allow overboring it to the larger size. A 390 block cannot be bored this far typically without weakening the block beyond repair.